I got this error message after start in Lightroom 5.7 "lightroom encountered an error when reading from its preview cache and needs to quit". It seems also catalog .lrcat disappears from disk. Also preview catalog .lrdata doesn't exists. So I try to reinstall Lightroom without success, I am still receiving the same error. How I can reset Lightroom to new catalog? I have backup of lrcat file, but I am not able to start Lightroom due to this error.
It seems solved. I have copied backup .lrcat to Lightroom data directory and I still have received error mentioned above. But when I doubleclick on .lrcat file in Explorer the catalog have been opened without problems.